Field of the Invention
The present invention relates to an imaging apparatus and a control method for the imaging apparatus, and more particularly, to an imaging apparatus to be used for ophthalmic diagnosis and treatment or the like and a control method for the imaging apparatus.
Description of the Related Art
The inspection of an eye portion has been widely conducted for the purpose of diagnosing and treating lifestyle-related diseases and diseases that are leading causes of blindness in early stages. As one of inspection apparatus for an eye portion, a scanning laser ophthalmoscope (SLO) that is an ophthalmic apparatus using a principle of a confocal laser microscope has been known. The SLO is an apparatus configured to perform raster scanning on a fundus of the eye with laser light which is measuring light and acquire a planar image of the fundus of the eye based on the intensity of return light of the measuring light with high resolution at high speed. Through the detection of only light having passed through a pinhole, the SLO can image only return light at a particular depth position to acquire an image with a high contrast compared to that of a fundus camera and the like.
Such an apparatus configured to acquire a planar image is hereinafter referred to as SLO apparatus, and the planar image is hereinafter referred to as SLO image.
In the SLO apparatus, it has become possible to acquire an SLO image of a retina with improved lateral resolution by increasing a beam diameter of measuring light. However, along with the increase in the beam diameter of the measuring light, there occurs a problem of decreases in an S/N ratio and the resolution of an SLO image of a retina due to an aberration of an eye to be inspected when the SLO image is acquired.
In order to solve the problem, there is developed an adaptive optics SLO apparatus including an adaptive optics system, in which an aberration of an eye to be inspected is measured by a wavefront sensor in real time, and aberrations of measuring light and return light thereof generated in the eye to be inspected are compensated by a wavefront compensation device. With such an adaptive optics SLO apparatus, it is possible to acquire an SLO image with high lateral resolution.
Further, the SLO image with high lateral resolution can be acquired as a moving image, and enables, for example, hemodynamics to be observed non-invasively. Therefore, through extraction of a retinal vessel from each frame, the moving speed of blood corpuscles in a capillary vessel and the like are measured. Photoreceptor cells can also be observed, and in this case, a focus position is set to the vicinity of retina outer layers, to thereby acquire an SLO image.
However, in a confocal image obtained by acquiring retina inner layers, a noise signal is strong owing to the influence of light reflecting from a nerve fiber layer, and hence it is difficult to observe a blood vessel wall and detect a wall boundary in some cases. In view of the foregoing, in recent years, a method involving obtaining scattering light by changing the diameter, shape, and position of a pinhole arranged in front of a photo-receiving unit and observing a nonconfocal image thus obtained has come to be used (Sulai, Dubra et al.; “Visualization of retinal vascular structure and perfusion with a nonconfocal adaptive optics scanning light ophthalmoscope”, J. Opt. Soc. Am. A, Vol. 31, No. 3, pp. 569-579, 2014). In the nonconfocal image, a focus depth is large, and hence an object having irregularities in a depth direction, such as a blood vessel, can be observed easily. Further, light reflected from the nerve fiber layer is not easily received directly, and hence noise can be reduced.
Further, the following has been found. Even in the case where photoreceptor cells in the retina outer layers are observed, hitherto, a photoreceptor outer segment is mainly imaged in the confocal image, whereas irregularities of a photoreceptor inner segment are imaged in the nonconfocal image (Scoles, Dubra et al.; “In Vivo Imaging of Human Cone Photoreceptor Inner Segments”, IOVS, Vol. 55, No. 7, pp. 4244-4251, 2014). Cells, in which the photoreceptor outer segment is lost but the photoreceptor inner segment exists in an initial stage of a photoreceptor cell disorder, are observed as follows: the cells can be observed to be lost in black in the confocal image, whereas the cells can be observed as a region with high brightness in the nonconfocal image.
As described above, in “Sulai, Dubra et al.; “Visualization of retinal vascular structure and perfusion with a nonconfocal adaptive optics scanning light ophthalmoscope”, J. Opt. Soc. Am. A, Vol. 31, No. 3, pp. 569-579, 2014”, there is a disclosure of a technology of acquiring a nonconfocal image of a retinal vessel through use of an adaptive optics SLO apparatus. Further, in “Scoles, Dubra et al.; “In Vivo Imaging of Human Cone Photoreceptor Inner Segments”, IOVS, Vol. 55, No. 7, pp. 4244-4251, 2014, there is a disclosure of a technology of concurrently acquiring a confocal image and a nonconfocal image through use of an adaptive optics SLO apparatus.
In the SLO apparatus capable of acquiring both a confocal image and a nonconfocal image, the signal intensity of a confocal signal is much larger. Therefore, in the case of displaying an acquired fundus image, the confocal image is generally displayed. However, in the case of observing a photoreceptor cell density and the like, the state of the photoreceptor cells can be observed more correctly by using the nonconfocal image in some cases. Therefore, in an apparatus configured to acquire both a confocal image and a nonconfocal image, it is necessary to appropriately switch between the confocal image and the nonconfocal image in consideration of information intended to be acquired by an examiner. However, it is necessary to select an intended image by comparing those images, which is cumbersome in actual inspection.